Toxic gases and vapors such as carbon monoxide, and other reducing agents can be detected by a single rather two substrate formulation of the invention and still pass UL 2034 effective August 2009 and current UL 2075 (which include system detector connected to a central panel and ventilation controls to turn on fans). These toxic compounds are difficult to detect accurately (plus or minus 5%) without false alarms without expensive technology such as instruments costing over $100 to $100,000 depending upon the accuracy and type of technology used.
Carbon monoxide (CO) has no smell, cannot be seen or tasted, but is very toxic. Such gases are hazardous to humans in automobiles, airplanes, mines, residential and commercial buildings, and other environments in which humans live, work or spend time.
For many years various chemical sensors have been used to detect the presence of toxins. For example, the use of palladium and molybdenum salts for carbon monoxide detection is described in Analytical Chemistry, Vol. 19, No. 2, pages 77-81 (1974). Later, K. Shuler and G. Schrauzer improved upon this technology by adding a third metallic salt component, which produces a self-regenerating catalyst that is short-lived. The catalyst disclosed in U.S. Pat. No. 4,043,934 uses the impregnation of a carbon monoxide-sensitive chemical catalyst solution into powdered silica-gel substrates to give detectors sensitivity to low concentrations of atmospheric carbon monoxide. While this system is effective in detecting carbon monoxide, it has not met with commercial acceptance due to the short functional life of the catalyst of less than 6 months.
It is generally recognized that, for a carbon-monoxide sensor system to be commercially useful in alarms and/or detectors, it must have a functional life of at least three years according to UL and, preferably 10 years or more. Tests have shown that the material described in U.S. Pat. No. 4,043,934 has a working life of only two to four months at room temperature and only three to four days at forty degrees Celsius (40° C.) in an oven.
U.S. Pat. No. 5,063,164 provided a method for detecting CO, which has a (useful) functional life of at least six years without calibration and it can withstand 50 C for 30 days in a chamber. However, these formulations, which used only one solid-state substrate does not provide adequate sensitivity under high humidity and high temperature conditions, which cannot resist false alarm limits as specified in the Underwriters Laboratories (UL) 2034.
U.S. Pat. No. 5,618,493 is an improvement over U.S. Pat. Nos. 5,063,164 and 4,043,934. U.S. Pat. No. 5,618,493 discloses carbon monoxide sensors, which met UL 2034 effective April of 1992 and October of 1995. Hereafter these above patents are incorporated herein by reference. U.S. Pat. No. 5,618,493 requires two solid-state bio-derived organometallic complexes coated onto a transparent porous silica substrate to produce CO sensors in order to satisfy the performance requirement listed under UL 2034 for residential and RV. The yellow solid-state bio-derived organometallic sensor detects CO well at ambient to low humidity conditions while the red sensor detects CO at ambient to high humidity conditions.
U.S. Pat. No. 5,618,493 by itself failed to meet the stringent sequential test requirements specified by the 2nd. Edition of UL 2034, which became effective October 1 of 1998. A new invention was made by Mark Goldstein, U.S. Pat. No. 6,251,344 issued on Jun. 26, 2001, hereafter incorporated herein by reference, was made to better control the humidity and remove potential interference chemicals, which might damage the sensor's sensitivity to CO. In or about November of 2003, Goldstein and Oum made additional improvements to U.S. Pat. No. 6,251,344, which described a means to further maintain relative humidity and certain air quality contaminates within a predetermined range for a predetermined period of time within a chamber, which is connected to the atmosphere by one or more small openings. The objective is to maintain a specific air quality including relative humidity (RH) within a predetermined range for extended period of time under real world conditions as well as extreme conditions specified by the UL 2034 and UL 2075. The controlled chamber(s) is contained within a housing that has one or more small openings to the atmosphere. The relative humidity control system also comprises at least one opening to a reservoir of chemicals including a salt with water in at least some solid or a solution containing at least some excess solid phase salt such as manganese chloride (MnCl2×4H2O), manganese bromide (MnBr2×4H2O), or mixtures of the two. The humidity control system uses a hydrophobic membrane to containing the liquid solution and solid salt(s) within the reservoir chamber but allowing gases and water vapor to exchange with the atmosphere in the sensing chamber where the CO sensors are located. This control system maintains predetermined RH % range (between about 15% and 90% or in most case even better such that the sensor system is able to meet UL 2034 and UL 2075) within the “Controlled Chamber” for a given temperature range regardless of the humidity variations in the outside environment, even allowing operation in condensing conditions. Such a system is referred as “reservoir,” hereafter. The reservoir allows the sensor formulations disclosed in U.S. Pat. No. 5,618,493 to meet the stringent sequential tests as required by the 2nd. Edition of UL 2034 by maintaining the humidity inside the micro-environment surrounding the sensors as close to ambient condition as possible. The controlled humidity condition prolongs the life of the sensors as they are subjected to extreme test conditions ranging from about −40° C. to +70° C. and from 7.5% RH to 95% RH sequentially without having to the replace any sensors from start to finish over a period of several months. In 95% humidity where condensing sometimes occurs depending on the location and operation, this reservoir prevents adverse effect from this condensing. And in low humidity conditions, it prevents the sensor from dehydrating. Although reservoir adds significant cost to manufacturing of the CO detectors, it is much needed along with a getter system in order to meet the UL 2034 requirements and to protect humans. (For extended periods of time such as 5 to 6 years depending sensor configuration and application, i.e. we set end of life for SIR at 5 years in passenger cars, truck and marine applications and 6 years in homes, apartments and hotels as well as other condition space.) With the improved chemistry, substrate, reservoir and getter, the MicroSIR will operate successfully for 10 years in conditioned space as defined by UL2034 and UL2075. This increased life and improved accelerated age testing is due to a combination of improvements and not one factor.
The present invention eliminates the need for two sensing disks in 90% of the single station market by the new chemical formulations of the chemistry as described in detail below for residential and other conditioned applications as specified in UL 2034 effective 2009 and current and proposed UL 2075. The chemistry was reformulated using a single MicroSIR Mini-size sensing improved substrate disk. The invention involves new formulations of sensing chemistry, specially combined and optimized so that only ONE instead of TWO sensing elements is enough to meet the requirement residential requirements specified under UL 2034 and live for over 10 years. Residential and commercial single station applications are 90% of the market and therefore most important from an economic point of view. The new single sensing chemistry formulations have been proven to perform better than both the regular-sized SIR sensors in the SIR assembly and to live longer (in fact twice as long in all accelerated age tests as shown below in detail. The micro-sized porous silica substrates are similar in composition to prior substrates but slightly different in pore diameter and structure, and have a thin coating on their surfaces of boron oxide, the coating having a thickness ranging between about 1 Angstrom and about 500 Angstroms. In some embodiments, the boron oxide may have a thickness of about 1 Angstrom to about 100 Angstroms. In some embodiments, the boron oxide layer thickness may be an average thickness (and generally, the slower the boron oxide layer is produced, the more uniform it is). The preferred embodiment using Quantum SPS substrate is 1 Angstrom to about 100 Angstroms; however for larger pore size material increase thickness is feasible such as was made by Robert Shoup U.S. Pat. No. 4,221,578 with pore size of about 1000 Angstroms to 10,000 Angstroms with average above 2000 Angstroms. Quantum's SPS has a typical pore diameter of 260 Angstroms with a surface area about 121.8 square meters per grams. The weight of the SIR disk is 0.054 grams. The density of amorphous SPS silica is about 2.2 grams/cc; however the SPS density due to the large number of hole is much less than 2.2 grams. It is 0.84 grams/cc. The SIR typical sized substrates are ˜0.100 inch thick and ˜0.230 inch in diameter as compared to the smaller mini-disks with boron oxide which are about ˜0.050 inch thick by ˜0.100 inch in diameter. The new sensing chemistry formulations can be applied to the substrates by either injection or immersion method. The injection method eliminates waste and has economic advantages because it has little or no waste and it uses much less of the more expensive materials (less than about ⅕ the cost of materials of the soak method).
The new single CO sensing element can replace the “dual CO sensing elements” in the current SIR CO alarm when the regular-size substrates are used. However, it requires UL approval testing from all over again and would not provide the advantages of longer life and better performance under extreme 30 day high temperature testing, which is an accelerated age test.
The time and money to obtain UL approval for switching from a dual to a single regular-sized CO sensing element is better justified when the single CO sensing chemistry is based on micro- or mini-sized substrates in MICROSIR; however, either size works well and passes all tests.
The new invention reduces the cost of sensor manufacturing by eliminating the need for two sensing disks to pass UL 2034 effective August 2009 residential section as well as by miniaturizing the sensing disk to require only 1/10 to 1/20 of the current starting materials for the sensor, which are expensive including cyclodextrin and its derivatives, palladium salts and molybdosilicic acid. The miniaturized single-sensing element requires less than 1/25 of the chemical sensing materials and less than 1/10 of the reservoirs materials (plastic, membrane, and chemical content). Bottom line, the new invention is expected to yield a net saving of 30 to 40% of the current manufacturing cost while exceeding or at least maintaining the same or better performance as the current SIR CO sensors which required TWO regular sized sensing elements. The Single-Sensing Micro-SIR has been shown to meet the latest UL 2034 for residential applications and live twice as long under accelerated age testing using ammonia as the life testing parameter. Several studies have shown that the limiting life mechanism is resistance of the sensing component(s) of the current sensor to ammonia, which has been found to average about 25 parts per million in a home (Helen H Suh, Petros Koutrakts, and John D. Spengler, Harvard School of Public Health, Journal of Exposure, Analysis and Environmental Epidemiology, Vol. 4, no. 1, 1994). However, it is desirable to design for extreme condition such as people who have several cats. In these cases, depending on the locations of the litter boxes and alarms, the ammonia concentration can be two to three times higher for some period of time. These cases have been shown to reduce the effective life of the sensor getter system of current SIR to a 6 year useful life.
Like the dual sensing elements counterpart, the new sensing element also needs a reservoir in order to meet the current UL 2034 standard and UL 2075 standard.
Here are a few examples of applications for the new Single-Sensing-SIR:
1. CO Alarms for Residential and Commercial single station and Residential and commercial system.
As mentioned above, the new Single-Sensing-SIR has been shown to meet the UL 2034 and 2075 for protecting human life against CO poisoning at homes, in commercial buildings, as well as in recreational vehicles and boats.
2. Visual CO Indicator
The new invention can be used as a visual CO detector for detecting the presence of CO. As visual CO detectors, the sensors made according to the formulations according to this invention require no power, no electronic, nor software. In the presence of CO (or at least a threshold level of CO), the sensor changes from one color to another color or one shade of color to another shade of color, e.g., tan-orange to dark-blue, at about 5-10% COHb. In the absence of CO, the sensors self-regenerate within a few hours to its original color and are reusable. These sensors also have over 6 years of operational life compared to 3 months for other technologies such as AIR-ZONE and DEAD-STOP. In addition to their amazing long sensor life, they also outperformed both AIR-ZONE and DEAD-STOP under wider range of relative humidity and temperature.
3. Digital CO Alarms and/or CO Instrumentation.
Results have indicated that the new Single-Sensing-SIR offers real potential for designing and manufacturing reliable, low cost CO alarms and potentially CO analyzers that allow digital display of the CO concentration on liquid crystal display (LCD). Most users do not know how to interpret CO levels and simply need to know the danger level. It may be an improvement to calculate the level of hazard, which is related to the percent carboxyhemoglobin in a human's blood. Once the hazard level is calculated, action plans can be announced by the alarm such as “open windows”, “call a service person” or “evacuate now and call from an outside phone”. These are two different action plans which would depend on the rate of rise as well as percent hemoglobin in the occupant's blood at the time.
In a preferred embodiment of a method of manufacturing a single sensor element, a substrate is coated first with boron oxide by heating the imbibed boric acid to over 160 C for about 2.5 hours. Then after cooling to room temperature, the substrate is coated with a supramolecular chemical reagent as described below to form a hybrid sensor. These hybrid sensors are referred to as the S6e and S66e sensor series. These sensors are well suited for detecting CO in the range of about 30 to 1,000 ppm. Other sensor formulations are better suited for detecting greater than about 1,000 ppm CO. The S6e and S66e sensor series re-gain their light transmittance in the presence of clean air (CO concentration <15 ppm) in about 1 to 2 hours. Any combinations of the three sensor series of S6e, or S66e with KYb to form a TWO element sensing system are referred to as a S34 series, as is done for marine, RV, or other unconditioned space applications.
Additional new CO sensing formulations that have increased sensitivity to CO after having been stored in low relative humidity for an extended period of time are referred to as the MO37-32b series, which occurs only with the boron oxide pre-coat of the substrate. The exact reason is not known.
Also the addition of ZnCl2 and ZnBr2 and/or MnCl2 and MnBr2 to replace a portion or all of the calcium chloride and calcium bromide in a group of the single sensor chemical formulation increases sensitivity under extreme aging conditions such 70 C for 30 days, which is an accelerated condition and very important for attaining the longest life sensor as possible.
The single sensor of the MICROSIR system of the present invention is small with a very low profile, which makes it suitable for many applications where small size is desired. The MICROSIR has at least seven additional advantages over the current SIR sensor system. These advantages of MICROSIR with improved substrate and chemistry over SIR include:
1. Lower cost per sensor manufacturing cost,
2. Better controlled-gas-path, therefore more accurate and more precision,
3. Better getter system therefore longer life (as shown by ammonia accelerated age tests the life resistance to basic gases such as ammonia is doubled), and
4. Better RESERVOIR SYSTEM THEREFORE BETTER Humidity CONTROL AT BOTH LOW AND HIGH (as shown by sensor response curves).
5. The MICROSIR “Edgeview” orientation of the sensor is faster and meets the European fire detection via CO also called enhanced smoke, and
6. More easily automated as the board of alarms use surface mount and MICROSIR is a surface mount part that attaches over surface mount optic after soldering.
7. Much smaller and therefore the alarm can be smaller and greener as there is less plastic and other materials as well as reducing shipping cost significantly.